In known arrangements of this kind, use is generally made of a fuel feed pump driven by the engine and this delivers the fuel from the supply container to the suction chamber of the injection pump during an operation thereof. These arrangements have the disadvantage that an additional unit, namely the feed pump, must be assembled and installed on the engine and, in addition, the drive to this feed pump has to be performed through additional drive transmitting means.
In order to avoid this drawback, in some known constructions, the fuel container has been arranged above the injection pump so that fuel can flow to the latter under gravity only. This makes a fuel feed pump in the suction conduit superfluous. This arrangement has, however, the disadvantage that when the supply container is installed in the engine, the gravity feed arrangement must be at a minimum elevation to ensure an adequate fuel feed to the injection pump. This involves consequent restrictions detrimentally affecting the capacity of the supply container and/or the overall size of the engine. It has also been proposed to provide a non-return valve in each of the suction conduit and return flow conduit of the fuel system, to enable the injection pump itself to act as the fuel feed pump and to be able to draw the fuel from the supply containers located therebelow. These constructions, however, have the disadvantage that, in consequence of the arrangement of the fully closing non-return valve being located above the injection pump, associated with the return flow conduit in that part of the return flow conduit which lies above the non-return valve, a fuel column may be set up which under certain conditions will very seriously obstruct the proper functioning of the system. For example, after an inadvertent emptying of the fuel supply tank, the conduit system will no longer be automatically evacuated of air because the fuel column which remains static in the return flow conduit above the non-return valve will prevent the escape of air during a fresh filling of the tank.
It is an object of the present invention to avoid these drawbacks in the known constructions and to provide an arrangement in which the operation of the injection pump itself can be relied on to draw the fuel from the supply tank without any constructional or functional limitations. This object is met in the present invention by the fact that a fully-closing non-return valve is incorporated in the suction conduit and that the non-return valve provided in the return flow conduit is of a construction such that when it is in its seated position, it permits a small flow of fuel between the return flow conduit and the injection pump.
Where using supply containers in which the lower-most part of the supply container is located below the injection pump and a manually operable auxiliary pump is provided in the suction conduit for filling the empty conduit system of the injection pump with fuel, in accordance with a special feature of the invention, the non-return valve associated with the suction conduit is installed in the auxiliary pump.
In systems of this character which have a fuel filter in the suction conduit, a very useful arrangement is acquired if the non-return valve, the auxiliary pump, and the filter are combined into a common unit.
In the case of injection combustion engines having a supply tank with a filling opening which is disposed above the injection pump, a simple and preferred embodiment of the invention resides in the arrangement whereby the non-return valve provided in the return flow conduit is arranged in such a way that it is disposed slightly below the filling part of the supply container.